In UMTS (Universal Mobile Telecommunications System) networks, for the purpose of improving spectral efficiency and further improving data rates, by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access), it is performed exploiting maximum features of the system based on W-CDMA (Wideband-Code Division Multiple Access). For the UMTS network, for the purpose of further increasing high-speed data rates, providing low delay and the like, Long Term Evolution (LTE) has been studied (Non-patent Document 1).
In the 3G system, a fixed band of 5 MHz is substantially used, and it is possible to achieve transmission rates of approximately maximum 2 Mbps in downlink. Meanwhile, in the LTE system, using variable bands ranging from 1.4 MHz to 20 MHz, it is possible to achieve transmission rates of maximum 300 Mbps in downlink and about 75 Mbps in uplink. Further, in the UMTS network, for the purpose of further increasing the wide-band and high speed, successor systems to LTE have been studied (for example, LTE Advanced (LTE-A)).
In addition, as one of promising techniques to further improve system performance of LTE system, there is inter-cell orthogonalization. For example, in the LTE-A system, intra-cell orthogonalization is achieved by orthogonal multiple access both in uplink and downlink. In other words, in downlink, user terminals UEs (User Equipments) are orthogonalized in the frequency domain. Meanwhile, for inter-cell, interference randomizing by 1-cell frequency reuse is a base as in W-CDMA.
Therefore, the 3GPP (3rd Generation Partnership Project) has studied Coordinated Multi-Point transmission/reception (CoMP) as techniques for actualizing inter-cell orthogonalization. In CoMP transmission/reception, a plurality of cells coordinates to perform signal processing of transmission and reception on a single or a plurality of user terminals UEs. For example, in downlink, studied are plurality-of-cell simultaneous transmission applying precoding, Coordinated Scheduling/Beamforming and the like. By applying these CoMP transmission/reception techniques, it is expected to improve throughput characteristics of user terminals UEs particularly positioned at the cell edge.
As an environment to apply CoMP transmission/reception, for example, there are a configuration (centralized control based on the RRE configuration) including a plurality of remote radio equipments (RREs) connected to a radio base station apparatus (radio base station apparatus eNB) with optical fibers or the like, and another configuration (autonomous decentralized control based on the independent base station configuration) of a radio base station apparatus (radio base station apparatus eNB). In the RRE configuration, as shown in FIG. 1, the radio base station apparatus eNB controls the remote radio equipments RREs in a centralized manner. In the RRE configuration, since the radio base station apparatus eNB (centralized base station) that performs baseband signal processing and control of a plurality of remote radio equipments RREs and each cell (i.e. each remote radio equipment RRE) are connected with baseband signals using optical fibers, the centralized base station is capable of collectively performing radio resource control among cells. Accordingly, in the RRE configuration, in downlink, it is possible to apply the method using high-speed inter-cell signal processing such as plurality-of-cell simultaneous transmission. In FIG. 1, transmission power of the remote radio equipment RRE is almost the same as transmission power of the radio base station apparatus (macro base station) eNB (high transmission power RRE).
As another environment to apply CoMP transmission/reception, as shown in FIG. 2, there is an overlay type network environment (heterogeneous environment) in which a plurality of remote radio equipments RREs is provided in a cover area of a radio base station apparatus (macro base station) eNB. In this environment, there are an environment (first heterogeneous environment) in which a cell of the macro base station eNB and a cell of each remote radio equipment RRE are different from each other i.e. cell identification information (cell ID) of the macro base station eNB and a cell ID of the remote radio equipment RRE are different from each other, and another environment (second heterogeneous environment) in which a cell of the macro base station eNB and a cell of each remote radio equipment RRE are the same i.e. a cell ID of the macro base station eNB and a cell ID of the remote radio equipment RRE are the same. In FIG. 2, transmission power of the remote radio equipment RRE is lower than transmission power of the radio base station apparatus (macro base station) eNB (low transmission power RRE).